In the case of ROOT_USER and ROOT_GROUP this loss of information was
solved with REAL_ROOT_USER and REAL_ROOT_GROUP but the issue still
remains open for all the other variables.

I would do it the very same way for all the user variables. The question
remains if we really need 100 different user variables which essentially
ends up as the same user in the end.

I asked myself the same question: Most packages can install their
executables with permission 555 and their data files with 444, so it
doesn't matter at all whom they belong to. I would even go as far as
leaving out the owner/group information from the binary package, except
for some special files like setuid/setgid binaries.